When I was in high school, someone took a photo of me in our school’s production of a Tom Stoppard play. For some reason my character was on her hands and knees in a ballroom-dancing outfit. One of my friends asked me if he could borrow the photo, to prove to another girl, he said, that I was in the school play. I never saw it again. I thought little of it. To me it was a funny photo of me in a pink dress. To the testosterone-charged boys among whom it circulated, it was a photo of cleavage. How do I know this? Years later my husband told me. He saw the photo.

I was lucky. There was just one photo as color copies were too expensive for school-age boys. The damage was pretty much limited to one zipcode. And I was dressed. But today, capturing and preserving a girl’s image is an extremely, globally high-risk proposition. One false step and you’re fed to the Internet trolls.

The British Internet Watch Foundation, which works with local police to investigate complaints of online child sexual abuse, recently combed through its database of sites specifically for images that looked like they were self-portraits or self-made videos. In a mere 47 hours they found more than 12,000 instances of girls who had taken provocative portraits or videos of themselves; when they examined the provenance of these photos, they found 88% of them had been lifted from other websites, including social media. That is, almost nine times out of ten, the self-portraits on the porny or otherwise offensive websites were used without the permission or knowledge of the people in them.

Why do young girls take pictures of themselves semi-naked or in come-hither poses? Theories abound. Some point to the mainstreaming of porn. Others attribute it to an increasingly sexualized society in which girls are saturated with images of women doing their best to inspire lust. There are theories that girls are just trying on various identities, playing at being adult. Some girls are coaxed into it by boyfriends, or lure into it by predators. Some are not thinking past the spur-of-the-moment snapshot on a camera phone. And then, too, there are teens who enjoy being sexual creatures and don’t care who knows.

A lot of the time, though, the photos are not meant to be sultry. Scroll through almost any teenage girl’s Facebook page — there are thousands that have zero privacy safeguards — and you’ll see photos of girls that, in another context, could be considered lewd. Facebook currently has a Bikini Jailbait page that has perfectly innocent pictures of cheerleaders and girls in school uniform and teens in their pjs on sleepovers and girls at the beach presented in a whole new way. That page offers a link to a more hardcore page for which you have to be 18 (which you prove by checking a box that says you’re 18). The fact that many of the girls in them are unaware of the use to which their images are being put apparently adds to the thrill.

How do these photos get circulated so widely? There is aggregating software, but most of the damage is done by other humans — not evil, psychopathic porn-moguls, but regular bored guys who like being popular. Never was this clearer than when Gawker unmasked a notorious internet troll known as Violentacrez (pronounced violent acres) on Oct 12. Violentacrez was known, and somewhat celebrated, for his offensive posts on the huge sprawling website Reddit.com. He created such Reddit pages as Rapebait, with photos of underclad underage girls, Creepshots, with covert photos taken of women’s behinds or breasts, and Boobies, with pictures of, well, not seabirds.

Violentacrez turned out to be not some monster but Michael Brutsch, a sad sack 49-year-old burly white guy who lives in Texas, worked at a boring job at a financial services agency, has a diabetic wife and a son who was about to join the Marines. When CNN pressed on him on what he was thinking, he seemed like a guy whose moral compass had never found north. “I have come to understand that things are inappropriate,” he said. “I am to some degree apologizing for what I did. I was playing to an audience of college kids.” This from a guy who started a Reddit section called Chokeabitch.

If lost, pathetic souls like Mr. Brutsch aren’t enough to take all the joy out of photography, then there are the several pages on Facebook which appropriate girls’ photos or tweets and annotate them with remarks about their sluttiness that range from snide to cruel to violent. On the “12 year old slut meme’s” page on Facebook, which is no longer active (the page owners signed off for good on October 11), two Australian men “Dom” and “James,” took it on themselves to run a westernized version of the Taliban using crude humor. Cartoons depicted sluts being pushed in front of trains, or Dora the Explorer talking about breasts. Their mission, as they saw it: “If you post slutty f—ing s— on facebook expect your photo to end up on here, then tagged in, then ripped to shreds by 120 thousand people. Chaos will continue. Go die.” More than 217,000 people clicked a button to say they liked the page and some continue to post comments. A sister page lives on, more simply but just as grammatically incorrectly known as “slutmeme’s.” Facebook has not closed down either page, but has removed some offensive material.

There are no good options for unmaking this cycle, in which girls — and some boys too — are encouraged to take and post portraits, then are exploited, and/or widely shamed for it. And there is no one villain, just a lot of people with a suboptimal understanding of the consequences of their actions, all of which cumulate in young girls being victimized.

But there is one clear message: once a picture goes online, it can never be unpublic again. It’s like trying to take out the tea once you’ve added boiling water. Perhaps it’s time to simply stop taking photos. Or at least make sure your child is fully aware of what he or she is doing. You might put it the way Internet Watch researcher Sarah Smith does: “If you have 100 friends on Facebook and each of them has 100 friends, are you really sure you want them all to see the photo you’re posting?”